Heat exchanger



July 20, 1948. R. E. BUCKHOLDT HEAT EXCHANGER 3 Sheets-Sheet 1 Filed May 9, 1944 ROBERT E. BUCKHOLDT J y 1943- R. E. BUCKHOLDT 2,445,471

HEAT EXCHANGER Filed May 9, 1944 3 Sheets-Sheet 2 ROBERT E. BUCKHOLDT July 1948- R. E. BUCKHOLDT HEAT EXCHANGER 3 Sheets-Sheet 3 Filed May 9, 1944 ROBERT E. BUCKHOLDT Patented July 20, 1948 2,445,471 HEAT EXCHANGER Robert E. Buckholdt, Salem, Ohio, assignor to The Salem Engineering Company, Salem, Ohio,

a corporation of Ohio Application May 9, 1944, Serial No. 534,723 2 Claims. (01. 257-246) This invention relates to heat exchangers and methods of making the same and more particularly to an improved heat exchanging tube and method of producing such tube as well as to improved complete heat exchanging assemblies utilizlng such tube either singly or in multiple;

The primary object of the invention is the provision of an improved heat exchanging tube which may be readily constructed of readily available and inexpensive stock materials but which, nevertheless, is highly efiicient in its normal and intended use and which possesses certain novel and advantageous characteristics as will be more fully explained hereinafter. In ac cordance with the preferred embodiment of this aspect of the invention, I construct the heat exchanging tube by first corrugating, doubling or pleating a metallic sheet or strip, and the material so treated is thereafter bent around a cylindrical form and fastened together in such manner as to form a complete tube having walls of uniform thickness and of deeply corrugated or fluted character. In this manner I provide as inherent features of the side wall of the tube a multiplicity of circumferentially spaced but longitudinally extending passages both inside and outside of the tube, a dividing wall between the inside and outside of uniformly thin and high heat conducting character, and box-like sections which contribute to the strength and rigidity of the completed tube. A further object of the invention is the provision of improved complete heat exchanging assemblies including confining passages for fluids both inside and outside of the primary heat exchanging tubes which utilize tubes of the general character outlined above.

These and other objects and advantages of the invention will become apparent upon consideration of the following detailed specification and the accompanying drawing wherein there is specifically disclosed certain preferred embodiments of the invention.

In the drawing:

Figure 1 is a side view of a heat exchanging tube constructed in accordance with the principles of the invention;

Figure 2 is a transverse sectional view of the tube of Figure 1, the view being taken along the line 11-11 of Figure 1;

Figure 3 is a fragmentary longitudinal section taken along the line III--III of Figure 2;

Figure 4 is an end view of bent or preformed stock preparatory to its fabrication into the principal body portion of the tube of Figure 1;

Figures 5 and 6 are side and plan views, re-

spectlvely, of a heat exchanging assembly utilizing the heat exchanging tube of Figure 1;

Figure 7 is a transverse sectional view of a modified form of heat exchanging assembly utilizing tubes each constructed in the manner illustrated in Figures 1, 2 and 3; and

Figure 8 is a sectional view taken along the line VIII-VIII of Figure 5.

In the drawing which illustrates the tube of theinvention in its preferred form and which illustrates the preferred method of fabricating the tube, reference numerals l0 and II designate lengths of conventional steel tubing which is of the seamless type or other type of good quality.

These lengths are aligned along their longitudinal axes but are spaced from each other along the common axis as indicated more clearly in Figure 1. The purpose of the lengths l0 and H is merely to provide a convenient arrangement for connecting either end of the tube of the invention to suitable fluid conducting means as will be readily apparent. Interconnecting the inner portions'of the tube lengths Ill and II is a tubular structure l2 which is formed by wrapping a length of sheet metal which has previously been bent into sinusoidal or pleated form (as indicated in Figure 4) about a suitable form or about the inner portions of the tube lengths l0 and l l with the meeting edges of the piece being welded along a seam as indicated at 13 in Figure 1. It is proposed to make the side wall of the tube l2 of stainless or other heat resisting steel and any suitable artifice may be resorted to to place the waves or pleats in the sheet material before the same is bent around to form the side wall structure of the complete heat exchanging tube. Also it should be understood that a multiplicity of circumferentially extending sections may be employed in completing the tube in place of the single piece illustrated in the drawing.

It should be apparent that a tube constructed in the manner outlined above is provided inherently with a multiplicity of circumferentially spaced but radially outward extending spaces (indicated on the drawing by reference numeral l4) each in open communication with the principal space inside the tube. In order to close off the ends of the spaces 14 the side walls (l5) .of each space M are bent together at their ends and welded or otherwise suitably joined along their meetin edges as at l-B. Whether the tube structure I2 is formed directly over the tube lengths l0 and II or is assembled on a suitable mandrel. etc., and subsequently transferred onto the tube 3 I lengths I and H, the edges of the inwardly directed end portions of the walls I which abut against .the outer surfaces of the tube lengths I0 and II are seam welded to the tubes I0 and II so that a permanent fluid-tight joint is obtained between the tube structure I2 and each of the tube lengths Ill and I I. I

It should be understood that the construction above described provides a heat exchanging tube in which the fluid contained within the tube is in effective heat exchanging relation with all of the inner surfacearea of the sheet metal making up the body of the tube. Since this sheet metal is doubled or pleated and has a substantial number of area components extending radially outward a substantial distance from the general inner circumference of the tube structure there is a materially increased surface area of metal in direct heat exchanging contact with the fluid contained within the tube. Also, because of the uniform thickness of the metal wall contiguous to or providing such surface area a uniform temperature gradient between the inside and outa side of the metal or vice versa as measured from any point on the inside (or outside) surface is effected whereby the metal of the tube is utilized to the maximum and the tube has equal heat exchanging eiflciency in either direction. Moreover, since the metal wall or walls dividing the fluids inside and outside the tube is uniformly thin a maximum rate of heat transfer results. Another singular advantage of the disclosed construction is that the 'circumferentially spaced walls I5 defining the spaces I4 form in themselves box-like beams and cooperate with each other to provide a box-like structure of substantial strength and rigidity. This arrangement reduces the weight of the metal required in the construction of the tube. It should readily be apparent that any stress tending to bend, deflect, or collapse the tube will be resisted by a number of webs (provided by the walls I5) which lie in the plane or substantially in the plane of the line of thrust.

Referring to Figures 5 and 6, which illustrate a representative use of the heat exchanging tube structure of Figures 1 through 4, reference numeral I8 designates an outer shell or housing which is adapted to snugly receive a heat exchanging tube constructed as illustrated in Figures 1 through 4. Thus, the general outer diameter of the heat exchanging tube I2 is only slightly smaller than the inner diameter of the housing I8. Housing It may preferably be pro-. vided by a length of seamless tube and as shown in the drawing it is provided at either end with enlarged fittings I9 and 20 from which extend in a lateral direction tubes 2| and 22, respectively. The latter are each provided with an integral connecting flange 23 to facilitate connection of the assembly to other fluid conducting elements.

As shown, the tube length I I which is connected to the body member I2 of the heat exchanging tube in the manner described above in connection with Figures 1 through 4 projects outwardly of the fitting I9 and a disk 24 apertured to receive the tube I I is welded about its periphery to the fitting I9 and about its aperture to the tube II to form a gas-tight connection as will be understood. Similarly the tube length III which is connected in a gas-tight manner to the opposite end of the heat exchanging tube I2 projects outwardly of the fitting 20 and to provide for a fluid-tight seal between the tube and the open outer end of the fitting 20 while allowing 4 for the longitudinal movement of the tube It relative to the fitting 20 as would be occasioned by the expansion and contraction of the heat exchanging tube I2 I provide a metallic bellows arrangement 23 which consists of a disk 23 of subwhich heated or cooled fluid passing through the inner tube I2 may impart heat to or absorb heat from a fluid which is circulated through the outer tube or housing I 8 by means of the connecting spurs 20 and 22. It should be observed that, in conformance with the principles explained above in connection with the tube I2 per se that substantial areas of heat exchanging walls are presented to both the fluid passing through the inner tube and the fluid passing through the housing I8. Moreover, this wall is uniformly thin throughout the whole of its area so that a maximum rate of total heat transfer is effected. Also, by reason of the even circumferential distribution or spacing of the interstices between the radially outward extending sections of the tube l2 the fluid streams passing both inside and outside of this tube are stratified throughout the whole of the lengths of the tube so that equal heating (or cooling) will be effected on all component parts of the streams. In this manner maximum utilization is had of the metallic wall surfaces of the principal heat exchanging element.

While the heat exchanging assembly described above is obviously susceptible of widely varying advantageous uses I have found the construction particularly suitable for the heating of air or gases and have so illustrated the invention. For this purpose, a gaseous fuel burner 28 is inserted in the tube I I, the burner being carried by a housing 29 which is suitably connected to the outer end of the tube I I as by means of a coupling 30, Fuel and air conduits 3| and 32, respectively, feed into appropriate channels contained in the housing 29 as is common in such constructions and it should be understood that upon ignition of the mixture issuing from the burner 28 the heat exchanging tube I2 will be filled with hot gaseous products of combustion which ultimately escape from the opposite end of the tube I2 through the tube length Ill. The fluid to be heated is circulated over the outside of the tube I2 and within the housing It! by entering at 22 and leaving at 2| or vice versa as will be understood.

In order to further insure the maximum utilization of the hot gaseous products of combustion (or other heating or cooling fluid) furnished the tube I2 I may provide a core 33 positioned within the tube I2 and having an outer diameter only slightly less than the general inner diameter of the tube I2 as indicated in Figures 5, 6 and 8. Core 33 may be of varying length but is preferably positioned centrally of the ends of the tube I2 and the operation or effect of the core 33 is to force all of the gases or fluid passing through the tube into the radially outward projecting interstices formed in the general outer wall of the tube. In this manner all of the gases or fluid is brought into efficient heat exchanging relation with the thin metallic walls of the tube. The core, which may be either of metallic or refractory material,

has the further advantageous effect of insuring the uniform circumferential distribution of the heating or cooling gases or fluids. Any suitable expedient may be employed to retain the core 33 in its proper position in the tube l2 as, for example, in the embodiment illustrated where the core is suspended by a rod 34 depending downwardly from a transverse rod 35 which spans the open upper end of the tube l0.

Figure 7 illustrates another possible advantageous use of the heat exchanging tube structure illustrated in detail in Figures 1 through 4. In this assembly an outer metallic casing 36 insulated as at 31 is so formed in cross-sectional outline to snugly receive a multiplicity of the tubes 12 which are preferably staggered or nested so as to provide for maximum Stratification and the maximum degree of wiping contact with the outer surfaces of the radially outward extending wall sections (I4 and I5) of the individual tubes [2. It should be understood that the spaces within the respective tubes 12 will be supplied with suitable heating or cooling gases or fluids as, for example, the products of combustion from individual bumers inserted in the ends of the tubes in the manner illustrated in Figures 5 and 6. Other fluid to be heated or cooled is circulated through the housing 36 outwardly of the spaces within the respective tubes 12.

It should now be apparent that I have provided improved heat exchanging assemblies and improved methods of constructing the same which fulfill the objects initially set out. By the use of light and thus relatively inexpensive materials I am enabled to readily construct highly eflicient heat exchanging assemblies which have a wide range of usefulness. Moreover, the inventions disclosed herein enable complete fluid heating or cooling assemblies including the required fluid passages to be fabricated from stock materials with a minimum of time and efiort.

The above specifically described embodiments of the invention should be considered as illustrative only as obviously many changes may be made therein without departing from the spirit or scope of the invention. Reference should therefore be had to the appended claims in determining the scope of the invention.

I claim:

1. Heat exchanging apparatus comprising a tubular structure having a metallic side wall formed of circumferentially spaced portions extending radially outward of the longitudinal center of said structure thereby providing a plurality of circumierentially spaced but axially extending fluid receiving pockets in open communication with the general space within said structure, a fluid deflecting member comprising an elongated body of refractory material positioned centrally in said structure and being operative to force fluid passing through said structure into said pockets, a fluid conducting casing having end walls enclosing said structure, said structure having fluid conducting components extending through said walls, and an axially yieidable metal seal between one of said components and the adjacent wall of said casing.

2. Heat exchanging apparatus comprising in combination an outer tube, an inner tube closely fitting within said outer tube and having a side wall formed of sheet metal provided with circumferentially spaced but axially extending undulations, the radially outward apices of said undulations lying substantially in contact with the inner surface of said outer tube, metal tube members fitting within the ends of said inner members with the radially inward apices of said undulations being in contact with the outer surfaces of said metal tube members, said metal tube members extending longitudinally outward of said outer tube, a disc interconnecting one end of said outer tube with one of said metal tubular members, a bellows interconnecting the opposite end of said outer tube with the other or said metal tubular members, and inlet and outlet ports in the side wall of said outer tube adjacent the ends thereof.

' ROBERT E. BUCKHOLDT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 690,055 Harris Dec. 31, 1901 897,661 Richman Sept. 1, 1908 1,437,039 Bingay Nov. 28, 1922 1,668,508 Kettering May 1, 1928 1,797,030 Steenstrup Mar. 17, 1931 1,840,724 Koehring Jan. 12, 1932 2,214,548 Chute et al Sept. 10, 1940 2,378,781 De N. McCollum June 19, 1945 2,379,017 McCollum June 26, 1945 2,404,647 McCollum et al. July 23, 1946 FOREIGN PATENTS Number Country Date 58,506 Switzerland Jan. 15, 1912 97.580 Switnerland Feb. 1, 1923 

